ST_NumPoints function

The ST_NumPoints function takes a geometry as an input parameter and returns the number of points that were used to define that geometry. For example, if the geometry is a polygon and five points were used to define that polygon, then the returned number is 5.

If the specified geometry is null or is empty, then null is returned.

Syntax

Parameter

geometry: A value of type ST_Geometry or one of its subtypes that represents the geometry for which the number of points is returned.

Return type

INTEGER

Example

A variety of geometries are stored in the table. The ST_NumPoints function determines how many points are within each geometry in the SAMPLE_GEOMETRIES table.


CREATE TABLE sample_geometries (spatial_type VARCHAR(18), geometry ST_Geometry)

INSERT INTO sample_geometries
  VALUES ('st_point',
           ST_Point (2, 3, 0) )

INSERT INTO sample_geometries
  VALUES ('st_linestring',
           ST_LineString ('linestring (2 5, 21 3, 23 10)', 0) )

INSERT INTO sample_geometries
  VALUES ('st_polygon',
           ST_Polygon ('polygon ((110 120, 110 140, 120 130, 110 120))', 0) )

SELECT spatial_type, ST_NumPoints (geometry) NUM_POINTS
  FROM sample_geometries

Results:


SPATIAL_TYPE    NUM_POINTS
--------------- ----------
st_point                 1
st_linestring            3
st_polygon               4